By the open by default list, do you mean this?:

I think it can only be other apps that go here. Or, if you mean have a manually typed link open an app then there are apps that do that. Not tried this though.
nostr:nprofile1qqstnr0dfn4w5grepk7t8sc5qp5jqzwnf3lejf7zs6p44xdhfqd9cgspzpmhxue69uhkummnw3ezumt0d5hszrnhwden5te0dehhxtnvdakz7qgawaehxw309ahx7um5wghxy6t5vdhkjmn9wgh8xmmrd9skctcnv0md0 is it possible to add a manually typed link to the open by default list for apps in nostr:nprofile1qqs9g69ua6m5ec6ukstnmnyewj7a4j0gjjn5hu75f7w23d64gczunmgpz4mhxue69uhhyetvv9ujumt0wd68ytnsw43q4gnztg?
By the open by default list, do you mean this?:

I think it can only be other apps that go here. Or, if you mean have a manually typed link open an app then there are apps that do that. Not tried this though.
No, links to open by default in this app.
https://developer.android.com/training/app-links/verify-site-associations
Then no, unless I'm not understanding. Only apps can be in that dialog, and you can't have it open a certain web page like on Windows or other OSes if that's what you're asking.
I mean this screen.
It's especially annoying with self hosted Jitsi instances, which the devs will never add in the integrated URL lists...

I believe this can only be configured by app developers. Users generally cannot add their own.
See: https://github.com/jitsi/jitsi-meet/issues/5199
You pinged the project account so another team member can correct me if I am wrong.
Yeah, that's what I thought, reasonable, but annoying for self hosted instances.
Is changes like this part of the scope of graphene?